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Validate handshake packet length early

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This commit is contained in:
Shane Freeder
2025-05-07 23:49:33 +01:00
parent b411a0fa09
commit 00016ba4e1
8 changed files with 106 additions and 3 deletions
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6
proxy/src/main/java/com/velocitypowered/proxy/connection/MinecraftConnection.java
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@@ -46,6 +46,7 @@ import com.velocitypowered.proxy.protocol.netty.MinecraftCompressDecoder;
import com.velocitypowered.proxy.protocol.netty.MinecraftCompressorAndLengthEncoder;
import com.velocitypowered.proxy.protocol.netty.MinecraftDecoder;
import com.velocitypowered.proxy.protocol.netty.MinecraftEncoder;
import com.velocitypowered.proxy.protocol.netty.MinecraftVarintFrameDecoder;
import com.velocitypowered.proxy.protocol.netty.MinecraftVarintLengthEncoder;
import com.velocitypowered.proxy.protocol.netty.PlayPacketQueueInboundHandler;
import com.velocitypowered.proxy.protocol.netty.PlayPacketQueueOutboundHandler;
@@ -368,6 +369,11 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
ensureInEventLoop();
this.state = state;
final MinecraftVarintFrameDecoder frameDecoder = this.channel.pipeline()
.get(MinecraftVarintFrameDecoder.class);
if (frameDecoder != null) {
frameDecoder.setState(state);
}
// If the connection is LEGACY (<1.6), the decoder and encoder are not set.
final MinecraftEncoder minecraftEncoder = this.channel.pipeline()
.get(MinecraftEncoder.class);

2
proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java
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@@ -47,6 +47,7 @@ import com.velocitypowered.proxy.connection.util.ConnectionMessages;
import com.velocitypowered.proxy.protocol.MinecraftPacket;
import com.velocitypowered.proxy.protocol.StateRegistry;
import com.velocitypowered.proxy.protocol.netty.MinecraftDecoder;
import com.velocitypowered.proxy.protocol.netty.MinecraftVarintFrameDecoder;
import com.velocitypowered.proxy.protocol.packet.AvailableCommandsPacket;
import com.velocitypowered.proxy.protocol.packet.BossBarPacket;
import com.velocitypowered.proxy.protocol.packet.BundleDelimiterPacket;
@@ -149,6 +150,7 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
MinecraftConnection smc = serverConn.ensureConnected();
smc.setAutoReading(false);
// Even when not auto reading messages are still decoded. Decode them with the correct state
smc.getChannel().pipeline().get(MinecraftVarintFrameDecoder.class).setState(StateRegistry.CONFIG);
smc.getChannel().pipeline().get(MinecraftDecoder.class).setState(StateRegistry.CONFIG);
serverConn.getPlayer().switchToConfigState();
return true;

2
proxy/src/main/java/com/velocitypowered/proxy/connection/backend/ConfigSessionHandler.java
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@@ -40,6 +40,7 @@ import com.velocitypowered.proxy.connection.util.ConnectionRequestResults.Impl;
import com.velocitypowered.proxy.protocol.MinecraftPacket;
import com.velocitypowered.proxy.protocol.StateRegistry;
import com.velocitypowered.proxy.protocol.netty.MinecraftDecoder;
import com.velocitypowered.proxy.protocol.netty.MinecraftVarintFrameDecoder;
import com.velocitypowered.proxy.protocol.packet.ClientboundCookieRequestPacket;
import com.velocitypowered.proxy.protocol.packet.ClientboundStoreCookiePacket;
import com.velocitypowered.proxy.protocol.packet.DisconnectPacket;
@@ -232,6 +233,7 @@ public class ConfigSessionHandler implements MinecraftSessionHandler {
final ConnectedPlayer player = serverConn.getPlayer();
final ClientConfigSessionHandler configHandler = (ClientConfigSessionHandler) player.getConnection().getActiveSessionHandler();
smc.getChannel().pipeline().get(MinecraftVarintFrameDecoder.class).setState(StateRegistry.PLAY);
smc.getChannel().pipeline().get(MinecraftDecoder.class).setState(StateRegistry.PLAY);
//noinspection DataFlowIssue
configHandler.handleBackendFinishUpdate(serverConn).thenRunAsync(() -> {

2
proxy/src/main/java/com/velocitypowered/proxy/network/BackendChannelInitializer.java
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@@ -51,7 +51,7 @@ public class BackendChannelInitializer extends ChannelInitializer<Channel> {
@Override
protected void initChannel(Channel ch) {
ch.pipeline()
.addLast(FRAME_DECODER, new MinecraftVarintFrameDecoder())
.addLast(FRAME_DECODER, new MinecraftVarintFrameDecoder(ProtocolUtils.Direction.CLIENTBOUND))
.addLast(READ_TIMEOUT,
new ReadTimeoutHandler(server.getConfiguration().getReadTimeout(),
TimeUnit.MILLISECONDS))

2
proxy/src/main/java/com/velocitypowered/proxy/network/ServerChannelInitializer.java
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@@ -58,7 +58,7 @@ public class ServerChannelInitializer extends ChannelInitializer<Channel> {
protected void initChannel(final Channel ch) {
ch.pipeline()
.addLast(LEGACY_PING_DECODER, new LegacyPingDecoder())
.addLast(FRAME_DECODER, new MinecraftVarintFrameDecoder())
.addLast(FRAME_DECODER, new MinecraftVarintFrameDecoder(ProtocolUtils.Direction.SERVERBOUND))
.addLast(READ_TIMEOUT,
new ReadTimeoutHandler(this.server.getConfiguration().getReadTimeout(),
TimeUnit.MILLISECONDS))

81
proxy/src/main/java/com/velocitypowered/proxy/protocol/netty/MinecraftVarintFrameDecoder.java
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@@ -19,10 +19,16 @@ package com.velocitypowered.proxy.protocol.netty;
import static io.netty.util.ByteProcessor.FIND_NON_NUL;
import com.velocitypowered.api.network.ProtocolVersion;
import com.velocitypowered.proxy.protocol.MinecraftPacket;
import com.velocitypowered.proxy.protocol.ProtocolUtils;
import com.velocitypowered.proxy.protocol.StateRegistry;
import com.velocitypowered.proxy.util.except.QuietDecoderException;
import com.velocitypowered.proxy.util.except.QuietRuntimeException;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.handler.codec.CorruptedFrameException;
import java.util.List;
/**
@@ -30,10 +36,31 @@ import java.util.List;
*/
public class MinecraftVarintFrameDecoder extends ByteToMessageDecoder {
private static final QuietRuntimeException FRAME_DECODER_FAILED =
new QuietRuntimeException("A packet frame decoder failed. For more information, launch "
+ "Velocity with -Dvelocity.packet-decode-logging=true to see more.");
private static final QuietDecoderException BAD_PACKET_LENGTH =
new QuietDecoderException("Bad packet length");
private static final QuietDecoderException VARINT_TOO_BIG =
new QuietDecoderException("VarInt too big");
private static final QuietDecoderException UNKNOWN_PACKET =
new QuietDecoderException("Unknown packet");
private final ProtocolUtils.Direction direction;
private final StateRegistry.PacketRegistry.ProtocolRegistry registry;
private StateRegistry state;
/**
* Creates a new {@code MinecraftVarintFrameDecoder} decoding packets from the specified {@code Direction}.
*
* @param direction the direction from which we decode from
*/
public MinecraftVarintFrameDecoder(ProtocolUtils.Direction direction) {
this.direction = direction;
this.registry = StateRegistry.HANDSHAKE.getProtocolRegistry(
direction, ProtocolVersion.MINIMUM_VERSION);
this.state = StateRegistry.HANDSHAKE;
}
@Override
protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out)
@@ -62,6 +89,38 @@ public class MinecraftVarintFrameDecoder extends ByteToMessageDecoder {
throw BAD_PACKET_LENGTH;
}
if (length > 0) {
if (state == StateRegistry.HANDSHAKE && direction == ProtocolUtils.Direction.SERVERBOUND) {
StateRegistry.PacketRegistry.ProtocolRegistry registry =
state.getProtocolRegistry(direction, ProtocolVersion.MINIMUM_VERSION);
final int index = in.readerIndex();
final int packetId = ProtocolUtils.readVarInt(in);
final int payloadLength = length - ProtocolUtils.varIntBytes(packetId);
MinecraftPacket packet = registry.createPacket(packetId);
// We handle every packet in this phase, if you said something we don't know, something is really wrong
if (packet == null) {
throw UNKNOWN_PACKET;
}
// We 'technically' have the incoming bytes of a payload here, and so, these can actually parse
// the packet if needed, so, we'll take advantage of the existing methods
int expectedMinLen = packet.expectedMinLength(in, direction, registry.version);
int expectedMaxLen = packet.expectedMaxLength(in, direction, registry.version);
if (expectedMaxLen != -1 && payloadLength > expectedMaxLen) {
throw handleOverflow(packet, expectedMaxLen, in.readableBytes());
}
if (payloadLength < expectedMinLen) {
throw handleUnderflow(packet, expectedMaxLen, in.readableBytes());
}
in.readerIndex(index);
}
}
// note that zero-length packets are ignored
if (length > 0) {
if (in.readableBytes() < length) {
@@ -141,4 +200,26 @@ public class MinecraftVarintFrameDecoder extends ByteToMessageDecoder {
}
return result | (tmp & 0x7F) << 14;
}
private Exception handleOverflow(MinecraftPacket packet, int expected, int actual) {
if (MinecraftDecoder.DEBUG) {
return new CorruptedFrameException("Packet sent for " + packet.getClass() + " was too "
+ "big (expected " + expected + " bytes, got " + actual + " bytes)");
} else {
return FRAME_DECODER_FAILED;
}
}
private Exception handleUnderflow(MinecraftPacket packet, int expected, int actual) {
if (MinecraftDecoder.DEBUG) {
return new CorruptedFrameException("Packet sent for " + packet.getClass() + " was too "
+ "small (expected " + expected + " bytes, got " + actual + " bytes)");
} else {
return FRAME_DECODER_FAILED;
}
}
public void setState(StateRegistry stateRegistry) {
this.state = stateRegistry;
}
}

12
proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/HandshakePacket.java
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@@ -106,4 +106,16 @@ public class HandshakePacket implements MinecraftPacket {
public boolean handle(MinecraftSessionHandler handler) {
return handler.handle(this);
}
@Override
public int expectedMinLength(ByteBuf buf, ProtocolUtils.Direction direction,
ProtocolVersion version) {
return 7;
}
@Override
public int expectedMaxLength(ByteBuf buf, ProtocolUtils.Direction direction,
ProtocolVersion version) {
return 270;
}
}

2
proxy/src/main/java/com/velocitypowered/proxy/server/VelocityRegisteredServer.java
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@@ -114,7 +114,7 @@ public class VelocityRegisteredServer implements RegisteredServer, ForwardingAud
server.createBootstrap(loop).handler(new ChannelInitializer<>() {
@Override
protected void initChannel(Channel ch) {
ch.pipeline().addLast(FRAME_DECODER, new MinecraftVarintFrameDecoder())
ch.pipeline().addLast(FRAME_DECODER, new MinecraftVarintFrameDecoder(ProtocolUtils.Direction.CLIENTBOUND))
.addLast(READ_TIMEOUT, new ReadTimeoutHandler(
pingOptions.getTimeout() == 0
? server.getConfiguration().getReadTimeout()